Rotary offset printing machine for multi-color printing

ABSTRACT

To improve color separation in printing machines in which at least two plate cylinders, each having an associated inking system and a wetting fountain, contact a single rubber cylinder, the wetting system associated with the plate cylinder is located behind the inking system - in the direction of rotation of the plate cylinder - and includes an axially oscillating roller and a contacting wetting application roller, each of which rollers has circumferential surfaces capable of being coated with a film of ink; alternatively, at least the second and each following plate cylinder has two wetting systems, one in advance and one behind the inking system, the advanced wetting system including an axially oscillating roller with a chrome surface. The circumferential speed of the application roller contacting the plate cylinder and located behind the inking system differs from that of the plate cylinder, preferably being slightly slower.

limited States Patet 1 Fischer [4 1 Sept. 2, 1975 ROTARY OFFSET PRINTING MACHINE FOR MULTI-COLOR PRINTING [75] Inventor: Hermann Fischer, Augsburg,

Germany [22] Filed: May 2, 1974 [21] Appl. No.: 466,284

3,455,238 7/1969 Gambella et al lO1/l48 3,467,008 9/1969 Domotor lOl/l48 3,508,489 4/1970 Norton 101/148 Primary Examiner-J. Reed Fisher Attorney, Agent, or Firm-Flynn & Frishauf [5 7] ABSTRACT To improve color separation in printing machines in which at least two plate cylinders, each having an associated inking system and a wetting fountain, contact a single rubber cylinder, the wetting system associated with the plate cylinder is located behind the inking system in the direction of rotation of the plate cylinder and includes an axially oscillating roller and a contacting wetting application roller, each of which rollers has circumferential surfaces capable of being coated with a film of ink; alternatively, at least the second and each following plate cylinder has two wetting systems, one in advance and one behind the inking system, the advanced wetting system including an axially oscillating roller with a chrome surface. The circumferential speed of the application roller contacting the plate cylinder and located behind the inking system differs from that of the plate cylinder, preferably being slightly slower.

3 Claims, 4 Drawing Figures PATENTEUSEP 21975 SI'IEU 1 BF 2 9 INKING SYSTEM 8 WETTING FOUNTAIN INKING SYSTEM %J PATENTED 35? 21975 saw 2 0F 2 ROTARY OFFSET PRINTING MACHINE FOR MULTll-COLOR PRINTING Cross reference to related applications:

U.S. Ser. No. 353,525, filed Apr. 23, 1973 US. Ser. No. 427,788, filed Dec. 26, 1973 US. Ser. No. 441,747, filed Feb. 12, 1974, all assigned to the assignee of the present invention.

The present invention relates to rotary offset printing machines for multi-color printing, in which the rubber cylinder or rubber cylinders have at least two plates cylinders in contacting engagement therewith, each plate cylinder having an inking system and a wetting system associated therewith.

It is difficult to carry out multi-color printing on ma' chines of this type, particularly in colors which have high contrast, over an extended period of time. The smooth, surface-coated papers frequently used, which do not have a high degree of ink absorption, some inks with high viscosity and adhesion, and smooth printing plates may cause remnants of ink to be transferred from a preceding to a subsequent printing plate, so that reproduction of colors with the initial purity is difficult to obtain. (For machines of this type see, for example, German Pat. No. 442,934).

It has previously been proposed (see US. Pat. No. 2,894,452) to locate a wetting fountain or wetting system at the second plate cylinder behind the inking system. When reference is made in the present specification and claims to ahead" and behind", this reference is deemed to be made with respect to the direction of rotation of the respective cylinder or roller. Thus, the wetting system associated with the second plate cylinder is located with respect to rotation of the sec ond plate cylinder behind, or after the inking system or inking fountain. The wetting liquid is applied to the last ink transfer roller which, in turn, is in contact with the axially oscillating ink roller. Due to the splitting of the medium transferred by the rubber cylinder or roller, at the zone of Contact of the rubber cylinder or roller, no intermediate layer of wetting liquid can build up. Thus, transfer of ink from a preceding to a subsequent plate cylinder cannot be prevented. A printing machine of this type may also have a wetting system located after, or behind the plate cylinder (see US. Pat. No. 2,894,453 the wetting liquid is applied by an axially oscillating roller, independent of the inking system or inking fountain, and the wetting system uses a fabric or cloth covered wetting application roller. The wetting liquid application roller rotates at the same circumfercntial speed as the plate cylinder. This prevents removal of any undesired ink spots or ink remnants transferred from the first plate cylinder, or the rubber cylinder, respectively, to the second plate cylinder. Such printing systems do, however, provide for better printing results than systems in which the wetting systems are independent from the inking system.

It is an object of the present invention to provide a multi-color rotary offset printing machine in which transfer of ink from a preceding to a subsequent plate cylinder is effectively prevented.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, in accordance with one embodiment of the present invention, a wetting system or fountain is provided independent of the inking system or fountain, and located behind the inking system; the wetting system includes an axially oscillating roller and a contacting wetting liquid application roller. The axially oscillating roller as well as the wetting liquid application roller both have a surface which carries a film of ink. A layer of wetting liquid is applied over the ink layer on the first plate cylinder. At the contact zone between plate cylinder and rubber cylinder, the more viscous and more tenacious ink displaces or supplants the corresponding portions of the layer of the less viscous, more easily flowing wetting liquid, and thus can be applied to the rubber cylinder. Yet, a film of wetting liquid is applied over the ink of the subsequent plate cylinder due to the wetting system located behind the inking fountain or system. This film of wetting liquid again forms an intermediate layer. Since, due to splitting at the printing zone, the thickness of the film of the ink decreases, the layer of the ink of the second color will be thicker than the layer of ink on the rubber cylinder having the first color. Thus, on the subsequent plate cylinder, the wetting film is displaced or supplanted by the ink of the second color upon printing and can trans fer ink to the rubber cylinder. Any ink of the first color, and derived from the first application, will form an in termediate emulsion layer, in which the emulsion includes ink and wetting liquid. Due to splitting, the layer is thinner, and thus transfer of ink 0f the first color from the rubber cylinder to the subsequent plate cylinder is prevented.

In accordance with a feature of the invention, the wetting liquid application roller of the wetting system which carries a layer of ink is driven at a circumferential speed which differs from the circumferential speed of the plate cylinder, so that a cleaning action will result, with respect to the plate, removing any undesired remnants of ink derived from the first plate cylinder.

In accordance with another feature of the invention, reliable wetting of the plate, in advance of application of ink, is ensured by utilizing an additional fountain system located in advance of the inking system, besides the wetting or fountain system located behind the inking system. A conventional fountain system is suitable, which includes at least a rubber application roller and an axially oscillating cylinder having a chrome surface, to which wetting liquid is applied by means ofa rubber ductor system, or by means of a spray arrangement. Any dry regions or zones at the second plate cylinder, which may be due to contact with the rubber cylinder, are thus wetted before ink is applied, so that no ink can be applied to the second plate cylinder at undesired positions.

The wetting systems may include rollers which accept the wetting liquid, and are conventional, and include a chrome surface oscillating wetting roller; or, in a preferred form, the wetting system located behind the inking system has an ink accepting surface which carries a coating of ink.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a highly schematic representation of the sequence and arrangement of rollers and cylinders for a rotary offset sheet printing machine;

FIG. 2 illustrates another embodiment of the sheet printing machine of FIG. 1;

FIG. 3 is a highly schematic diagram of a continuous web multi-color rotary offset printing machine; and

FIG. 4 illustrates another embodiment of the machine of FIG. 3.

The printing system of FIG. I has a sheet feeding cylinder 13, in contact with a sheet feeding cylinder 7 which tranfers sheets s to a printing counter cylinder 2, which is again in contact with a sheet removal cylinder 3. Rubber cylinder 4 contacts one surface of sheet s applied to the sheet feeding cylinder l by a gripping mechanism, not shown, and transferred between cylinder 1 and printing cylinder 2. Rubber cylinder 4 has two plate cylinders 5, 6 associated therewith. Printing cylinder 2, rubber cylinder 4, and plate cylinders 5, 6 have the same diameter. Each plate cylinder 5, 6 has an inking system, or inking fountain 7, 8 associated therewith which includes axially oscillating rollers, and ink supply, a ductor roller, or a spray system, and intermediate application and transfer rollers, as known in the art. The inking system can be conventional and is therefore shown only schematically; other types of inking systems than those schematically shown, may be used.

In accordance with the present invention, a wetting system 9, I is located behind (with respect to the direction of rotation of the plate cylinders 5, 6, respectively) the respective inking systems 7, 8. The wetting system is of the ink accepting type, and includes, each, an axially oscillating roller l5, 16, having a surface of copper, for example by having a copper-plated surface, and a contacting wetting application roller l7, l8 having a rubber surface. The wetting liquid is sprayed on the axially oscillating, copper-surface roller l5, 16.

Various types of printing layouts, particularly those which are difficult to print require reliable wetting of the plate cylinder. In order to effect such reliable wetting, the modified embodiment of FIG. 2 may be used in which an additional wetting system 1], 12 is provided, respectively associated with the plate cylinders 5, 6, and located in advance of the inking systems 7, 8. These wetting systems 11, I2 may be conventional. Wetting system 11, for example, includes a lifting roller, intermittently operating, and a ductor roller. The wetting system located in advance of the inking system may, however, be constructed similarly to the ink accepting system 9', as indicated schematically in connection with wetting system 12.

The wetting systems located in advance, and behind the inking system may be conventional, and thus may be of the conventional only water-accepting type, that is, including a chrome surface axially oscillating roller and a rubber application roller. The wetting liquid can be sprayed on the chrome roller, or applied by an intermittently operating lifting roller, by dipping into a trough, or the like.

The wetting systems located behind the inking system, however, that is, wetting systems 9', 10', preferably include a roller capable of accepting ink. These rollers are preferably driven at a circumferential speed which differs from that of the associated plate cylinder 5, 6, respectively, for example having a slightly lesser speed.

The arrangement of the wetting systems can be used with various types of printing apparatus. This arrange ment may be used not only with the system illustrated in FIGS. 1 and 2, but may be used with multiple printing systems of this type. located sequentially (with respect to sheet travel) in series. They may be connected by means of transfer drums having the same, or double the diameter of the cylinders; they may cooperate with a common printing cylinder of double diameter. The

arrangement of the wetting systems may also be used for printing on both sides of the sheet, in which case two rubber cylinders will be used in contact with each other (so that printing cylinder 2 will be replaced by a rubber cylinder); the arrangement may also be used with systems in which more than two plate cylinders contact one rubber cylinder. The showing and the explanation in connection with FIG. 1 is intended to be explanatory of an example only.

FIGS. 3 and 4 illustrate, schematically, printing systems for double-sided printing of four colors on continuous webs. Each one of the printing systems includes two rubber cylinders having, each, two plate cylinders associated therewith. FIG. 3 illustrates a continuous web 20 which is guided between the two rubber cylinders 21, 22. Rubber cylinder 21 has plate cylinders 23, 24 associated therewith. Rubber cylinder 22 has plate cylinders 25, 26 associated therewith. Each one of the plate cylinders 23, 24, 25, 26 apply, initially, two colors of ink. The web 20, now printed with two colors, on both sides, is then guided to the second printing system which has rubber cylinders 27, 28, with which plate cylinders 29, 30 and 31, 32, respectively, cooperate. As seen in FIG. 3, the rubber cylinders and the plate cylinders have the same diameter. Each one of the plate cylinders has an associated inking system 33, 34, 35, 36, indicated, schematically, by the pointed triangle, and which may be similar to the inking systems 7, 8 of FIG. 1. Wetting systems 41, 42, 43, 44 and 45, 46, 47, 48, respectively, are further associated with the plate cylinders 23-26 and 29-32, respectively. The wetting systems 4l48 are of the type discussed in connection with FIG. I, that is, they include a wetting roller, oscillating axially, having a surface capable of accepting ink, and a rubber application roller.

The system of FIG. 4 is similar to the system of FIG. 3, except that two wetting systems are used for each plate cylinder, one in advance and one behind the inking system. Thus, each plate cylinder has the wetting systems 4l44 associated with the first printing unit and 4548 associated with the second printing unit, all the wetting systems being located behind the inking systems 3336 and 3740, respectively. Further, additional wetting systems 49, 50, 51, 52 and 53, 54, 55, 56, respectively, are located in advance of the respective inking system. The wetting systems 4I44 and 45 48' may be conventional, and may be wetting systems capable of accepting ink, or capable of accepting wetting liquid, typically water, only.

Various changes and modifications may be made within the scope of the inventive concept, and the invention may be applied to various types of rotary offset printing machines and is not limited to the specific ar rangement of plate cylinders, rubber cylinders and printing cylinders, of sheet or web transport shown and described, but may be applied to any type of such printing systems. Features described in connection with any one of the embodiments may be used, similarly, in connection with any of the other embodiments.

I claim:

1. In a rotary offset printing machine for multi-color printing having at least two plate cylinders contacting a rubber cylinder, each plate cylinder having an inking system associated therewith and applying ink to the respective plate cylinder,

the improvement wherein each plate cylinder has two wetting systems associated therewith. one located with respect to the direction of rotation of the plate cylinder behind the inking system. and the other in advance of the inking system. the wetting systems being separate and independent from said inking system. and

wherein each wetting system comprises at least two rollers, one being an axially oscillating wetting roller having wetting liquid applied thereto and having an essentially unyielding surface capable of accepting ink. and a wetting liquid application roller in Contact with the axially oscillating roller and the plate cylinder and having a yielding surface capable of accepting ink. said rollers. in opera tion. having a film of ink thereon;

and wherein the circumferential speed of the wetting the roller having the copper surface.

l l l 

1. In a rotary offset printing machine for multi-color printing having at least two plate cylinders contacting a rubber cylinder, each plate cylinder having an inking system associated therewith and applying ink to the respective plate cylinder, the improvement wherein each plate cylinder has two wetting systems associated therewith, one located - with respect to the direction of rotation of the plate cylinder - behind the inking system, and the other in advance of the inking system, the wetting systems being separate and independent from said inking system, and wherein each wetting system comprises at least two rollers, one being an axiaLly oscillating wetting roller having wetting liquid applied thereto and having an essentially unyielding surface capable of accepting ink, and a wetting liquid application roller in contact with the axially oscillating roller and the plate cylinder and having a yielding surface capable of accepting ink, said rollers, in operation, having a film of ink thereon; and wherein the circumferential speed of the wetting liquid application rollers contacting the respective plate cylinder differs from the circumferential speed of the plate cylinder to provide slip between the plate cylinder and the contacting wetting application roller.
 2. Printing machine according to claim 1, wherein the speed of the wetting application roller is less than that of the associated plate cylinder.
 3. Printing machine according to claim 1, wherein the wetting system train located in advance of the inking system includes at least a rubber wetting liquid application roller, an axially oscillating roller having a copper surface, and means applying wetting liquid to the roller having the copper surface. 